(a) Field of the Invention:
The present invention relates to water-soluble cutting fluids useful for cutting or grinding work, and more specifically to water-soluble cutting fluids featuring suppressed deterioration by microorganisms. Still more specifically, the present invention is concerned with water-soluble cutting fluids resistant to yeast-like fungi. The term "water-soluble" as used herein should be interpreted in a broad sense as commonly accepted in the present field of art, so that it can be taken as an equivalent to "water-miscible" and can embrace "water-dispersible" therein.
(b) Description of the Related Art:
Water-soluble cutting fluids useful for cutting or grinding metal contain, as components, a mineral oil, a fatty oil, an extreme-pressure additive, a surfactant, a defoaming agent, a metal anticorrosive, an antiseptic, a fungicide, and the like. These components are mixed at a ratio suitable to the end use. For use, such water-soluble cutting fluids are generally diluted 10-100 fold with water. The thus-diluted solutions are called "coolants".
A coolant is required to exhibit good performance not only in cutting or grinding performance (i.e., primary performance) but also in working efficiency and the like (i.e., secondary performance). Secondary performance requirements include good rust resistance, slow deterioration and easy maintenance, harmlessness to the human body, low foaming tendency, etc.
Among these secondary aspects, it is a very important to avoid deterioration by microorganisms for the following reasons. If putrefaction of a coolant develops due to deterioration by microorganisms, both first performance and second performance capabilities are reduced and moreover, the working environment is deteriorated by an unpleasant odor. Further, growth of fungi in the coolant may lead not only to lowered first and second performances but also pipe clogging in a recirculation system.
As a method for preventing deterioration of such water-soluble cutting fluids by microorganisms, it has heretofore been the practice to add a bactericide.
However, such a bactericide may exhibit good activities against certain specific microorganisms but may not be effective against another type or other types of microorganisms, resulting in the problem that the breadth of applicability is restricted. Moreover, there is another problem in that the bactericide may decompose or otherwise become inactive in a short time, so that long-term bactericidal effects are extremely poor. In addition, the use of the bactericide at a high concentration results in the problem that it gives adverse effects to the human body, especially severe skin irritation which may induce skin roughness or chapping, dermatitis, etc. When a bactericide is used, care must always be exercised to maintain constant concentration, leading to a further problem of increased manpower and cost.
Incidentally, the invention disclosed in Japanese Patent Publication No. 40720/1986 features the addition of a diamine represented by the below-described formula to a water-soluble cutting fluid whereby the tendency of deterioration of the water-soluble cutting fluid by microorganisms can be improved: ##STR1## wherein R.sub.1 means a hydrogen atom or an alkyl, alkenyl, cycloalkyl, alkylaryl, aralkyl or aryl group having up to 24 carbon atoms, R.sub.2 denotes an alkyl, alkenyl, cycloalkyl, alkylaryl or aryl group having up to 24 carbon atoms, and n stands for an integer of 4-18.
Examples of the diamine, which are disclosed in the patent publication, include dibutylaminododecylamine, ethylaminoethylamine, di-2-propenylaminoethylamine, cyclohexylaminoethylamine, 3,5-dimethylphenylaminobutylamine, benzylaminooctylamine and phenylaminobutylamine.
Further, the invention disclosed in Japanese Patent Publication No. 4880/1988 resides in the addition of an amine represented by the below-described formula to a water-soluble cutting fluid so that the tendency of the water-soluble cutting fluid to deteriorate through corruption by microorganisms can be reduced: EQU RO(CH.sub.2).sub.n NH.sub.2
wherein R means an alkyl, alkenyl, cycloalkyl, alkylaryl, aralkyl or aryl group having up to 24 carbon atoms, and n stands for an integer of 2-18. Exemplary amines in this prior art publication include 2-ethylhexyloxypropylamine, lauryloxyethylamine, 2-ethylhexyloxydodecylamine, lauryloxydibutylamine, cyclohexyloxypropylamine and benzyloxypropylamine.
The amines proposed in the above patent publications are effective against a wide variety of bacteria and fungi. However, their bacterial activities against yeast-like fungi are weak. The current situation is therefore that they cannot bring about satisfactory effects against the deterioration of water-soluble cutting fluids caused by yeast-like fungus or fungi.